1. Field of the Invention
The present invention relates to a fuel injector for an internal combustion engine.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 3-78562 discloses a fuel injector in which the injection hole is made slit-like. The injection hole has an almost uniform relatively small height and a width which is gradually narrowed inward at a predetermined included angle. Therefore, the injected fuel therefrom becomes a spray in a flat triangular shape which has a relative small thickness. Such a fuel spray of a flat fan shape can be favorably atomized and mixed as nearly all of the fuel comes into sufficient contact with the air. In the fuel injector, the injection hole is communicated directly with a fuel reservoir downstream of the seat portion of the valve body, and the fuel is injected through the injection hole as the pressure of fuel within the fuel reservoir is increased.
The height, width, and included angle in the slit-like injection hole are important to define the fuel spray shape. To form a desired shape fuel spray, the injection hole must be made very precisely. A laser system and the like is usually used to make a slit-like injection hole. However, such a making of the injection hole is not easy and thus many production failures can occur.
Accordingly, if the injection hole is directly made in the injector body, many injector bodies in which a production failure occurs must be thrown away. This causes the yield of injector body, which is relatively expensive, to deteriorate and the manufacturing cost of the fuel injector to increase considerably. To solve these problems, a tip portion of the injector body is separate from the injector body, and the downstream portion of the fuel reservoir and the injection hole can be formed in the tip portion. Therefore, even if a production failure of the injection hole in the tip portion occurs, only the tip portion must be thrown away prior to mounting to the injector body, and thus the manufacturing cost of the fuel injector does not increase considerably.
However, when the tip portion is separate from the injector body, a slight deviation of the tip portion in mounting to the injector body causes the downstream portion of the fuel reservoir formed in the tip portion to not correspond to the upstream portion thereof formed in the injector body, and a step portion is formed within the fuel reservoir. When fuel flows from the upstream portion of the fuel reservoir to the downstream portion thereof, fuel impinges to the step portion within the fuel reservoir.
In the step portion side within the fuel reservoir, a turbulent flow of fuel is produced as the fuel impinges to the step portion, and the pressure of fuel within the downstream portion of the fuel reservoir becomes low. Therefore, even if the injection hole is favorably formed, depending on the position of the step portion, a uniform pressure of fuel does not act all over the injection hole and thus a desired fuel spray cannot be formed.